Bassman Ten in for service

[Yoda]

The fuse in the amp is a 3A, back panel calls for a 2.5 Amp. I have not powered it up yet but will soon.

[Yoda]

Got it fired up slowly using a variac with a light bulb current limiter. Unloaded B+ voltage is 501v and I have -45v on both pins 5 of the power tube sockets. With tubes in I get 417v on the power tube plates with 25.5 mA of current draw, everything stable over a 10 minute period so far.

ETA: The light bulb current limiter was choking the amp a bit. Plugged straight into the variac at 117v the real plate voltage is 483v with 38mA of current draw. Thats 18.5 watts per tube, or ~61% max dissipation. Perfect!

[xtian]

I got a Bassman 10 in today for service, and am happy to see your photo:

Mine also has the clipped white wire exiting the grommet from the doghouse in the center of your photo. Thanks for the confirmation!

[Yoda]

I got a Bassman 10 in today for service, and am happy to see your photo:

Mine also has the clipped white wire exiting the grommet from the doghouse in the center of your photo. Thanks for the confirmation!

I immediately remembered this wire upon reading your reply, very interesting!

I didn’t know what to make of it and technical info on the Bassman Ten is extremely limited so I just left it alone because the particular amp I worked on was about as original as they come so part of me thinks it left the factory that way. Seeing your comment makes me feel better about that. Fender did some interesting things during the CBS era that’s for sure.

[Stevem]

Fender switched to that wire rap from what I guess was the more expensive foil rap shielding they use to build with.

[Yoda]

Fender switched to that wire rap from what I guess was the more expensive foil rap shielding they use to build with.

We’re not talking about the white wire wrapped around those other wires as some kind of shield, we’re talking about this plastic wire:




If you search gut shots of this amp you’ll see the same clipped white wire coming from the dog house in the amps that are mostly or all-original whereas people seem to remove it in the Bassman Tens that they’ve modded/updated.

[solderhead]

I own an original B10. I would pop the hood to answer some of the questions that have come up, but it's in storage now. I only kept it around as an indictment of how bad the Fender build quality had become during the CBS era.

I do remember some odd things though -- when they placed those small ceramic caps between the 5881 grid and capacitor (not on the schematic) they passed the leg of the cap through the pin 8 socket and soldered the lead of the cap to the socket near the cap's body, and that same lead was left long and passed through the pin socket and was soldered directly to chassis ground -- with the result that the power tubes had no other cathode/ground connection than through the lead of the cap. All of the tube current passed through the tiny little leads of the anti-oscillation capacitors. Fender was cheaping-out by using the capacitor leads to avoid spending money on an inch or two of cathode wire when manufacturing the amps.

Could that white plastic wire that is cut-off at the chassis grommet have been used as a fishtape? It looks like they may have used the white plastic cable as a pull-through cable to pull the green wire up to the doghouse. Then they just cut off the white plastic fishtape flush with the grommet when they were done with it.

[Smitty]

I suspect they standardized the cap board and found it was cheaper to put it on all them and then cut it off for models that didn't use it. It would have been used for vibrato on an amp like the Super Reverb.

[Yoda]

I suspect they standardized the cap board and found it was cheaper to put it on all them and then cut it off for models that didn't use it. It would have been used for vibrato on an amp like the Super Reverb.

That’s actually a pretty logical theory given Fender’s affinity for assembly line-type innovations.